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Topic: Dragonfly, Powered by Canon Lenses (Read 12191 times)

Dragonfly is an innovative, multi-lens array designed for ultra-low surface brightness astronomy at visible wavelengths. Commissioned in 2013, the array is proving capable of detecting extremely faint, complex structure around galaxies.

According to Cold Dark Matter (CDM) cosmology, structure in the Universe grows from the “bottom up”, with small galaxies merging to form larger ones. Evidence of such mergers can be seen in faint streams and filaments visible around the Milky Way Galaxy and the nearby M31 galaxy.

Image Copyright University of Toronto

But the CDM model predicts that we should see more of this structure than is currently observed. However, images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure.

Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.

images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure [...] Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.

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Is this using commercially available lenses with non-commercially available coatings?

images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure [...] Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.

?!

Is this using commercially available lenses with non-commercially available coatings?

No, from the article I linked to

Quote

...the latest generation of Canon lenses features the first commercialized availability of nano-fabricated coatings...

I chatted with one of the guys on this project over on the CloudyNights forums a couple months back. Back then, he said the current version of DragonFly had 8 commercially available Canon EF 400mm f/2.8 L II lenses, however that they were in the process of adding four more for a total of 12. Their ultimate goal was to get up somewhere round 20-24. To achieve that, they had to redesign the mount that holds the lenses. The original version was a squareish contraption, and I think the new approach uses something more modular, some kind of hexagonal or circular cells that can be attached to each other.

I'm one of the astronomers who put the thing together - thanks for the interest!We use standard SBIG off the shelf astronomical cameras as detectors. The lenses are fast enough, and the integration times long enough, that read noise is negligible even with only modest cooling of the detectors.

We've published a paper that describes the thing; this is the publicly available version, for those who are interested:http://arxiv.org/abs/1401.5473As you may notice we're mostly concerned with scattered light; we measured the point spread function out to ~1 degree (Fig 6) and found that it is amazingly well controlled (this was recently confirmed by another group, who compared our results to a wide range of other telescopes).

We've had some science results out this year, too - and we just put out a press release on the discovery of seven very faint galaxies (which might be why CR posted it today!). The reason why we went with Canon is that I'm a Canon shooter (with a special interest in dragonflies..) and I was aware of the quality of the updated lenses. I know lenses and Bob knows telescopes, so it all worked really well.

Other groups have used Canon lenses for astronomical purposes, but typically just to cover a wide area of sky - not to detect very low surface brightness emission, beyond the reach of reflecting telescopes.Anyway, sorry for rambling on - it's a fun project!

Thanks Pieter! I read your paper with interest. Dragonfly is a very cool project from an astronomical perspective, but there are also several points that could be of interest for the more general Canon shooter / astrophotographer:

The optics are found to be essentially diffraction limited, at least <1 degr of the center, which is quite amazing. This means that the image sensor will give increasingly sharp images all the way to a pixel pitch of about 0.63 µm before out resolving the lens. This is 6.8 times smaller than the effective pixel size of a 7D and would imply a 839 MP APS-C or 2.18 GP FF sensor! The lens resolution is likely decreasing from diffraction limited away from the central regions, but this sets the upper usable limit for sensor resolution. In practice, there will be other things limiting the resolution, like turbulence in the atmosphere (for anything shot at a distance).

Strehl ratios between 0.2-0.8 (where 1.0 is 'perfect') indicates that the lens provides a very high contrast (which we knew). I wonder if the Canon designers have deliberately tried to keep the effective point-spread function constant with wavelength (reducing colour mis-matches in images), deacreasing the Strehl at short wavelengths.

The precise focus of the lens is strongly temperature dependent: a temperature difference as small as 1C gives a significant shift in focus. This is mostly relevant for exposing an extended period, like in astrophotographical applications.

The foot of the 400/2.8L IS II provided by Canon shows significant flexure so that care must be taken during tracked exposures.

For those wanting more images, I found two papers accepted by ApJL providing such for M101:

The project seems to have left the start-up phase only recently (they are apparently still extending the array), so I'm sure we can expect more results soon. Note, however, that they are targeting the faint structures around galaxies, and with only two broad-band filters ('r' and 'g'), meaning the images will probably not be as spectacular aesthetically as narrow-band imaging of more photogenic nebulae. But when they're done with the galaxies perhaps they can put in some nebular filters instead, and give us the most surface-brightness sensitive images of nearby nebulae

Actually, surveying for nearby supernova remnants in H-alpha might be a pretty interesting project scientifically in itself for this Dragonfly.

And then we have the transiting exoplanets, of course, but that has probably been covered pretty well by the already mentioned super-WASP projects and the upcoming NASA TESS mission.